The present invention relates to FM-CW (frequency modulated-continuous wave) radar equipment, more particularly to FM-CW radar equipment which enables to detect a failure in a radio-frequency circuit of the equipment.
In FIG. 1, there is shown a conceptual schematic diagram of an RF (radio-frequency) circuit of FM-CW radar equipment. The equipment provides a transmitter 1 and a receiver 2. In transmitter 1, the amplitude modulation is carried out where a modulation signal 3 consisting of a triangle wave is modulated by a carrier signal 10. The modulated signal frequency is multiplied n-times by a frequency multiplier 11. The multiplied signal is then amplified by a power amplifier 13, to be transmitted by an antenna 4 through a non-illustrated transmission filter.
Moreover, a branching filter 12 is provided in transmitter 1. A part of signals transmitted from transmitter 1 are branched to input to receiver 2.
The transmitted signal is reflected by an object and then received by receiver 2 through an antenna 5. The signal is then forwarded to receiver 2, and input to receiver 2 through a non-illustrated reception filter.
The received signal is amplified in an amplifier to input to a mixer 21. In mixer 21, therefore, a beat frequency signal is output corresponding to the phase difference between the transmitted signal branched from branching filter 12 and the received reflection signal.
More particularly, the magnitude (amplitude level) of the beat frequency signal corresponds to the phase difference of the transmitted signal and the received reflection signal. This corresponds to the distance between transmitter 1 and the reflection object. Thus the distance to the object can be measured.
The beat frequency signal is divided into intermediate-frequency (IF) by a frequency demultiplier 22 and is output from receiver 2. The beat frequency signal divided into IF is used in a non-illustrated circuit to convert into a signal corresponding to the distance.
Meanwhile, as an application, FM-CW radar equipment is applicable for collision prevention equipment housed in a vehicle. In such a case, a failure of FM-CW equipment may possibly affect a human life. It is therefore important to detect a failure in FM-CW equipment in any case.
Among prior arts for detecting failure in such FM-CW radar equipment, an art is disclosed in the official gazette of Japanese Unexamined Patent Publication No. Hei-11-52052. In this disclosure, there is introduced a method for detecting an equipment failure by observing the level of an amplitude modulation signal. This prior art is based on the fact that an amplitude modulation signal disappears in IF output of a mixer when a failure occurs in any unit of the equipment.
In this prior art, however, an amplitude level of the modulation carrier disperses to a great extent. It is therefore difficult to adjust the level within a certain criterion range.
It is therefore an object of the present invention to provide FM-CW radar equipment which solves the aforementioned problem in the prior art.
In the present invention, there is applied a technological concept different from the conventional arts. The inventor has obtained the configuration of the present invention based on the following phenomenon: a noise level output from a mixer 21 changes when a failure occurs in an RF circuit of the equipment; there is a region generated by electronic characteristic of transmitter 1 in which a noise level changes as the frequency changes; and also there is a region generated by electronic characteristic of receiver 2 in which a noise level does not change, irrespective of the frequency.
The basic configuration of FM-CW radar equipment in accordance with the present invention includes a noise-level extraction circuit in RF circuit, and a comparator for comparing an output of the above-mentioned noise-level extraction circuit with a predetermined criterion value. The equipment is configured so that an alarm signal is output when the output of the noise-level extraction circuit becomes smaller than the predetermined criterion value.
Preferably, the noise-level extraction circuits include a first noise-level extraction circuit in the transmission side of the RF circuit; and a second noise-level extraction circuit in the reception side of the RF circuit. The comparators include a first comparator for comparing the output of the above-mentioned first noise-level extraction circuit with the first predetermined criterion value; and a second comparator for comparing the output of the second noise-level extraction circuit with the second predetermined criterion value.
Further, preferably, the circuits for extracting a noise level include a first noise-level extraction circuit in the transmission side of the RF circuit, and a second noise-level extraction circuit in the reception side of the RF circuit. There is provided a single comparator to which an output of the first noise-level extraction circuit or an output of the second noise-level extraction circuit is selectively input, respectively to compare with the predetermined first criterion value or the second criterion value.
Still further, preferably, in either of the aforementioned embodiments, the first noise-level extraction circuit at the transmission side consists of a low-pass filter transmitting a signal in a first frequency bandwidth in which the noise level changes with frequency; and the second noise-level extraction circuit at the reception side consists of a band-pass filter transmitting a signal in a second frequency bandwidth in which the noise level substantially does not change with frequency.
Still further, preferably, the aforementioned second frequency bandwidth is located in higher frequency region than the first frequency bandwidth.
Further scopes and features of the present invention will become more apparent by the following description of the embodiments with the accompanied drawings.